This invention relates to a protective integral cover for a hard cover book and to a new and improved method for covering hard cover books.
Heretofore, hard cover books have been covered either in leather, cloth, paper or vinyl because only these materials can be readily formed and stamped in a way that would provide a quality cover for the book. In mass produced hard cover books, only cloth, paper and vinyl have been economically feasible. It has not heretofore been possible to use polypropylene as a book covering material because polypropylene sheets do not cut well, and do not form well in the gutters, i.e. the grooved hinges between the edge binding and the stiff side panels of the book cover. It is essential in a quality book cover that all edges be sharp and clean, that all portions of the cover be free from wrinkles, and that the gutters be completely smooth, but not shiny and it must be free of bubbles and heat distortion. A wrinkled, shiny or bubbly gutter detracts from the appearance of the book and is unacceptable. Moreover polypropylene tends to stick to the hot lettering stamp used to impress letters into the cover of the book, and polypropylene sheets tend to block or stick together so that when stacked they cannot be readily separated into individual sheets without some effort. Thus polypropylene simply did not measure up to a quality book cover material. Nevertheless the desirability of polypropylene from the environmental standpoint is great.
It has been found that if a polypropylene homopolymer is properly mixed with a proper amount and type of calcium carbonate and extruded, the resultant blended film (1) can be easily cut, (2) will form well in the gutters, (3) will have very little tendency to stick to the hot lettering stamp, and (4) the blocking problem can be minimized.